Sunday, August 31, 2014

Smoke from a Distant Fire

It's been a while since we've had an airmass push into Utah from the northwest, but it happened last night and it brought the smoke from a distant fire, partially obscuring the Wasatch Mountains this morning.

The smoke is from fires in Oregon and possibly northern California.

Source: NIFC
The 2-day loop below shows the push of high pressure and northwesterly flow into Utah overnight.  

And with the smoke came a bump in PM2.5 concentrations overnight, as if we don't get enough crappy air in the winter.

Source: Utah DAQ
It will be nice when those fires are out and the northwest returns to a source of pristine air!

Saturday, August 30, 2014

Signs of a Wet August and the Start of Fall

Thanks to an active series of monsoon surges the Wasatch are remarkably lush right now, with firm, moist trails (at least on north aspects) and a jungle-like feel (by Utah standards).

Adding to the ambiance was a light, steady shower in the early afternoon.  That shower was produced by an approaching upper-level trough in the westerly midlatitude flow – a harbinger of the return of the storm track as fall approaches (hooray!).

Indeed signs of fall are beginning to appear, with a few trees already beginning to pack it in, even at these lower (7000–8000 ft) elevations.

Boy scouts are working to realign the trail in the area we were in today.  Although it's great they are out working on the trails, we wondered why the realignment was needed and the existing trail was in pretty good shape.  All we could figure was that there's a desire to move the trail away from the stream that runs down the canyon.  However, it appeared this was being done at the expense of mature aspens.

Hopefully those trees were diseased or dead as otherwise it's a damn shame to lose them.  

Friday, August 29, 2014

The Long Life of "Tropical" Cyclone Cristobal

Living a long life typically requires hitting the genetic jackpot, living in a relatively safe and healthy environment, taking care of yourself, and then perhaps just being plain lucky.  Swiss mountain guide Ulrich Inderbinen provides such an example.  He climbed the Materhorn 390 times, summited it a final time when he was 90, climbed 13,000 foot peaks in his 90s, worked until he was 95, and passed away this summer at 103.  Not too shabby.

Although not as far out there on the longevity limb as Ulrich Inderbinen, "Tropical" cyclone Cristobal, which moved poleward off the west east coast of North America this week, lived a pretty good life, benefiting from a caterpillar-to-butterfly-like metamorphosis from a tropical cyclone into a midlatitude cyclone as it moved into the North Atlantic.  

At the beginning of the loop below, Cristobal is barely a glint in his parent's eye and just a weak cluster of thunderstorms associated with a tropical easterly wave between Africa and the Lesser Antilles, islands that form the eastern edge of the Caribbean Sea.  He moves eastward and eventually experiences a quick birth and adolescence, growing into Hurricane Cristobal near the Bahamas.

The poleward movement of a hurricane into the cool waters of the higher latitudes often results in cyclone death, but Cristobal pulled off the necessary metamorphosis to extend his life, transitioning into an extratropical cyclone off the coast of the northeast United States and southeast Canada.  Such a transition requires a favorable large-scale environment, and Cristobal was fortunate to find himself in that environment as he crested the hill of middle age.  

Reborn as an extratropical cyclone, Cristobal is enjoying a productive maturity and is expected to survive until he reaches Iceland (see lower panel below).  

That's a lifetime from easterly wave through tropical cyclone to extratropical cyclone that spans nearly 2 weeks and almost 60º of latitude, and a remarkable example of one type of tropical–extratropical interaction that occurs during late summer and fall in the Northern Hemisphere.  

Thursday, August 28, 2014

Regionally, Mother Nature Can Still Bring It

There is a nice article in the latest EOS, a publication of the American Geophysical Union, discussing the remarkable ice cover on the upper Great Lakes this past spring [See Cold Water and High Ice Cover on the Great Lakes in Spring 2014 by Clites et al. (2014), unfortunately paywalled unless you are an AGU member and login with your membership account].
Source: Clites et al. (2014)
Some tidbits from the paper:
  • Lake Superior wasn't completely ice free until June 6th.  Yeah, June!
  • At the end of April, 51% of Lake Superior, 23% of Lake Huron, and 10% of Lake Michigan were still ice covered. 
  • In the 40-year period of record at the end of April, the previous record on Lake Superior was 30%, in only a few years was significant ice observed on Lake Huron, and at no time was their significant ice on Lake Michigan.
A quick look at data from NCDC shows that this past Dec–Apr was the coldest in Michigan (which flanks Lakes Superior, Michigan and Huron) since 1920 and the 4th coldest on record.  The period is a dramatic outlier during the 40-year period of good ice-cover records.

Source: NCDC
During the same period, globally averaged temperatures were the 6th warmest on record, illustrating that Mother Nature can still bring it, but only regionally.

Source: NCDC

Wednesday, August 27, 2014

Wet, But How Wet?

What an August it has been.  Lots of rain and relatively cool days.  Nobody can complain this year.

Although it has been wet, a quick look at the weather records suggests that the area has seen wetter.  Let's start with the Salt Lake City International Airport.  Through yesterday, the accumulation for August 1–27 was 1.77 inches (green line), well above average (brown line).  That ties it for 8th amongst the wettest August 1–27 periods.  However, there have been similar periods in past years that were much wetter, including 1968 when 3.66 inches fell (blue line).

Source: NWS
Given the fickle nature of monsoon convection, however, observations at a point can sometimes be misleading.  Let's look at a few other stations.

Alta has been deluged this August with an accumulation of 5.33" so far, which puts it just behind 1983 (5.97").  There is some missing data for the period though (black dots), including yesterday, which will add to the total.  On the other hand, the data at this location is very spotty.  For instance, there is no data for August 1–27, 1968, which was the wettest such period at some nearby stations.  Thus, we can't make any definitive conclusions here, but we can say it's certainly been very wet.

Source: NWS
If we head a bit west, the situation at Tooele looks pretty similar to Salt Lake City.  This year's August 1–27 period is well above average with 1.99" of rain, but still behind the 1968 deluge year.

Finally, if we go down to Utah County, records from the school that shall not be named show August 1–27 to be wet with 2.54", but not record setting.  Here, long-term records are also spotty (1968 is missing, for example).

I suspect if we had a dense and complete precipitation observing network covering 50 years we would find that August 1–27,  2014 ranks in the top 10 such periods at most locations in the Salt Lake area and perhaps near record levels at a few spots that have really gotten walloped by the thunderstorms.  During the past 50 years, August 1–27, 1968 may be the wettest such period on record, although I've only looked at a few stations and there could be some exceptions to this given the hit-and-miss nature of monsoon thunderstorms.

If you are interested in records for the month, we still have 4 days left.  Although there are no big monsoon surges in the offing, we have a chance of some showers and thunderstorms later today and perhaps we'll see something pop up later in the period.  Some sites could add to their totals.

Tuesday, August 26, 2014

Showers and Thunderstorms, But Where and When?

Where is the coldest air in the continental United States?  Well, if we go up to 500 mb, which sits about 18,000 feet above sea level at an area where the presence of cold air is frequently associated with thunderstorm formation, it's over northern Utah and eastern Nevada, with a close 2nd for the upper Dakotas (technically the analysis below is a 6-hour forecast, but let's call it good).

GFS Forecast 500-mb temperature at 1800 UTC 26 Aug 2014
Accompanying that pocket of cold air is a weak 500-mb trough centered over Nevada.

With the pocket of cold air, monsoon moisture, and surface heating, thunderstorms are likely across much of Utah this afternoon and are even possible overnight thanks to the dynamical forcing of the upper-level trough (you may have heard some last night).  When it comes to storms like these, however, their development and evolution occurs over periods of at most a couple of hours.  Therefore, forecasting the where and when is pretty much impossible until you see 'em on radar and even then the skill of predicting location and intensity declines rapidly after 30 minutes.  Sometimes the presence of an upper-level trough helps as it can organize the convection, but in this case, the trough is fairly weak and thus it's evolution also has low predictability.

Perhaps in the future we'll have pinpoint forecasts of thunderstorms at long lead times.  A new high-resolution forecast model known as the High Resolution Rapid Refresh (HRRR) may provide modest advancement and is featured in today's forecast discussion from the National Weather Service, although you get the gist of the uncertainty from the initial statements.
The last I checked, the hRR was to become operational in late September.  I'm not sure if that schedule will hold.  I don't expect it will be a panacea for predicting convection of the type we have today, but I'm hoping it will be useful for forecasting mountain precipitation at short (≤18 hours) lead times this winter.

Monday, August 25, 2014

Freshman Orientation

Today is the first day of Fall Semester at the University of Utah.  Welcome to all the students, new and continuing.  Even those on double secret probation (you know who you are).

If you are new to Utah, consider yourself fortunate.  We have had a remarkably cool and wet August, especially over the past several days.  Average high temperatures for the month so far are 3.3ºF below average, and we've had 1.57" of rain at the Salt Lake City Airport compared with an average of 0.69".  It's been especially cool the past several days when many of you have arrived, moved into your dorms or apartments, and told the parents adios.  Over the past two days, we haven't even hit 80ºF!

Source: NWS
If you are coming from out of state, this weather is isn't normal.  The average high for today is 88ºF, with a record of 100ºF.  When you look for a new place for the next academic year, don't just find good roommates, find an air conditioned unit too.

Saturday, August 23, 2014



Friday, August 22, 2014

Flirting with Snow

Source: NWS
If you search hard enough in the forecast grids for the Wasatch Mountains this morning, you can find a few locations with a predicted rain/snow mix for tomorrow (see above).  

The cause is an approaching mid-latitude trough that will be over northern Utah tomorrow.  

Temperatures on Saturday are low enough that snow levels in the GFS drop to as low as 10,500 feet.

This is also a situation in which heavy precipitation can develop, which often results in a temporary lowering of the snow level.  Further, the gold-standard ECMWF model is even cooler than the GFS, so don't be surprised if you see flakes on the high peaks this weekend.

Thursday, August 21, 2014

Wet Streak to Continue

It's been a great month for plants in northern Utah and the unsettled weather will likely continue through Saturday.

For all intensive purposes, our wet weather began in late July.  Since July 28th, measurable precipitation totaling 1.47 inches has been recored on 10 days, with trace amounts on 3 additional days.  That's about double the climatological average for the period (around 0.77 inches).

Over the past 30 days, precipitation across most of northwest Utah is now running 150% or more above average and in some instances more than 300% of average.

Source: NWS
More rain is coming.  In addition to the unsettled monsoon weather, a broad mid-latitude trough is moving into the area and is expected to interact with the monsoon moisture and further stimulate precipitation late Friday and Saturday.

So, we should have a very impressive precipitation anomaly relative to average for the 30-day period ending Saturday.  What a great summer! 

Wednesday, August 20, 2014

Holy California Thunderstorms Batman!

The American Meteorological Society Mountain Meteorology Conference is in San Diego this week.  Early in the week, it was an extremely difficult assignment to sit in a dark conference room and suffer death by powerpoint when it looked like this outside.

In general, interesting weather avoids meteorologists like the plague and you'd figure that that would be especially true in San Diego which probably has the most benign weather in the U.S.  In August, in particular, the average rainfall is only 0.06".  Today, however, we we treated to a glimpse of a rare beast: The California Thunderstorm.

It didn't look like much on radar, but those are some fairly high returns exceeding 50 dBZ just offshore.

Source: NCAR/RAL
Lightning?  Yeah, plenty of strikes, primarily offshore.

Most of the locals just continued their outdoor recreation, but with thunder and lightning in the area, I headed in quickly from my morning walk.  Only a couple of weeks ago 13 people were injured and 1 killed by lightning at Venice Beach.

With the fun and games over, I'm back suffering death by powerpoint again...

Tuesday, August 19, 2014

A Forecast Gone Bad

A few days ago I announced the arrival of a monsoon break and suggested that it would likely remain dry for several days (see Arrival of the Monsoon Break).  Well, we got a few days of dry weather, but a monsoon surge snuck into Utah last night and rain is falling this morning across northern Utah.

Source: NCAR/RAL
This forecast bust provides a nice example of how subtle changes in the large scale forecast can bite you in the rear during the monsoon.  The GFS forecast from 6Z last Friday called for an elongated upper level trough to extend from the eastern Pacific into northern California, placing Utah in a relatively dry southwest to westerly flow aloft.

Instead, the trough verified along the California coast, placing Utah in southerly to southwesterly flow that tapped into moisture from the monsoon region.  Really, this was a full blown forecast bust for all of the southwest U.S. it is also far wetter in Arizona than forecast a few days ago.

The surge of moisture into northern Utah last night shows up well in integrated precipitable water measurements from the Salt Lake City International Airport.  Note how values spike from 1.5 cm yesterday afternoon to nearly 3 cm this morning.
So, moisture has returned to northern Utah.  Looks like we can go a few more days before turning the sprinklers on.

Sunday, August 17, 2014

Gaining Perspective on the Central Wasatch

Eighteen years in Salt Lake City and I've never hiked up Clayton Peak, which lies above Brighton in upper Big Cottonwood Canyon.

I did it today and discovered that there might be no better place to sit and think about how the topography influences the snow climate of the Wasatch Mountains.

The image below, in particular, was taken to highlight the high terrain surrounding Little Cottonwood Canyon (LCC, click to enlarge).  Mt. Timpanogos to the south is higher than any of the topography surrounding LCC by a couple hundred feet, but it is an elongated ridge.  As a result, it sees heavy snowfall primarily when the flow crosses that ridge (i.e., out of the south or southwest), but not so much in other patterns.  The island of topography surrounding LCC, however, while famous for snowfall enhancement in northwesterly flow, usually helps out some during storms featuring a wide variety of flow directions.  The great diversity of storms that can affect the high terrain surrounding LCC is one of the reasons why Alta and Snowbird are so snowy (the Snowbird tram is indicated below, while Mt. Baldy sits above most of the lift served terrain at Alta.

Although it is pretty snowy in Big Cottonwood Canyon (BCC), it actually hooks around the higher terrain surrounding LCC.  In addition the topography to the north and northeast of the canyon is lower than found around LCC.  Thus, although BCC certainly gets the goods, the climatological snowfall is not quite as great as found in LCC.

If you turn around and look east, you peer down on Deer Valley, which is just past the small lakes in the photo below.  Climatologically downstream of the bulk of the Wasatch Range, it's little wonder why Deer Valley gets considerably less snow.  They like the groomers over there anyway.

After summiting and heading down, it was a great relief to discover that the avalanche hazard was low.

More about the weather and climate of the Wasatch Mountains and how to find great snow in other ranges throughout the world can be found in my forthcoming book Secrets of the Greatest Snow on Earth.

It's now finished and going to the printer, and should be on the street in November, although you can pre-order from Amazon now.  The publisher (University Press of Colorado) did an unbelievable job and I'm really excited about how it's going to look in both print and e-book versions.

Saturday, August 16, 2014

July Was Hot and Cold

For some reason, I've always been fascinated with the climate record for July.  Perhaps it's because it is the hottest month of the year at most (but not all) locations.  This year was particularly interesting.

Let's start in Utah.  As we've discussed previously (see Near or Above Average Temperatures Are an Easy Bet in July), you can usually count on above average temperatures in July in Utah, and this year didn't disappoint.  On a statewide basis, the average temperature was 75.5ºF, 3.0ºF above average and the 7th warmest July on record.  The last July with a statewide mean temperature below the 20th century average was 1997.  

Source: NCDC
At the Salt Lake city International Airport, we only had two days with a temperature above 100ºF (July 14 and 23rd, both of which hit 103ºF), and we had a really nice cool down during a big monsoon surge at the end of the month (high temperatures of 76, 82, and 85ºF on July 29, 30, and 31, respectively). Nevertheless, sustained high temperatures for most of the month gave us a mean temperature of 81.9ºF, 4.4ºF above the 1948–2000 average and the 6th warmest July since records at the airport began in 1948.

Source: NCDC
We've discussed previously that the apparent cooler temperatures this July compared to last July is at least partly a result of a high temperature sensor bias at the airport last summer (see Was July 2014 Cooler Than July 2013) and indeed when one looks the average temperature for the North Central Utah Climate Zone, which encapsulates the Wasatch Front, one finds that the mean July temperature for this summer was just 0.4ºF cooler than last summer.  In addition, although last summer was hot, for this climate region, 2002, 2003, 2006, and 2007, were clearly hotter.  Nevertheless, both summers were clearly well above the 20th century average.

Source: NCDC
 Nationally, July was really interesting, with persistent ridging over the Pacific Northwest and troughing over the upper midwest leading to record high temperatures over the former and record cool temperatures over the latter.  Temperatures along the Oregon and northern California coastal zone were the highest on record, whereas they were the coolest on record from Arkansas to southern Lake Michigan.  Most of the west saw above average (in some cases well above average) temperatures), whereas much of the midwest saw below average (in some cases well below average) temperatures. 

It must have been a remarkably pleasant July (by climatological standards) in the midwest.  

Friday, August 15, 2014

Arrival of the Monsoon Break

Mostly sunny skies over the Salt Lake Valley are a harbinger of things to come
Change is underway over northern Utah as drier air gradually moves into the region.  Integrated precipitable water values, which indicate the total water vapor in the atmosphere, have been declining the past two days and have dropped to below 2 cm as drier air moves in.
Source: ESRL
Yesterday, we still had a few showers and thunderstorms around (congrats to you Utah County and other area residents who enjoyed a late-night splurge), but they should be widespread today and more confined to areas of high terrain.  Further, the models show relatively dry air in place over the next few days.  The time-height section below is based on forecast profiles of relative humidity (color fill) over the Salt Lake City for the next 180 hours (time increases to the left).  For the most part, it's fairly dry.
Waxes and wanes in monsoon moisture and precipitation are known as monsoon surges and breaks, respectively.  We've experienced some impressive surges in the past couple of weeks, but it now appears the switch has been flicked and we'll be experiencing a monsoon break.

Thursday, August 14, 2014

Very Lush!

My personal weed patch (a.k.a. lawn) is looking unusually lush for mid August with just a few patches of brown to be found.  

It's a real pity that invasive annual grasses have taken over the landscape in the foothills or it might be a bit greener around town.  

Here's an interesting plot for you from the National Weather Service that shows the departure from average precipitation over the past 14 days.  Northeast Nevada has had a "climatological deluge" with 600+% of average precipitation.  What I find interesting is that northern Utah and the northern Wasatch Front have also been fairly wet, with anywhere from about 110–600+% of average, but if this analysis is to be believed, portions of the Sevier Desert to our south have been remarkably dry.  Although such spatial variability is not unusual during the monsoon, in this case it could reflect a lack of radar coverage and gauge data in the area, so perhaps someone out there could dig into what gauges are available and let me know if they really have gotten the shaft during this wet period.  

The computer models suggest that the fun and games are almost over.  Enjoy the relatively high humidity and any showers that we get today.  

Tuesday, August 12, 2014

The Red Sunset

As the sun sets in the sky, its color often transitions from yellow to orange or even red.  Why?

Sunlight is comprised of visible light of all colors and wavelengths.  Superman really didn't get his powers from the "yellow sun" because the sun isn't yellow, it's white.

The white color reflects the fact that sunlight is comprised of light across the entire visible spectrum, which we can break down using the Roy G. Biv acronym where R=Red, O=Orange, Y=Yellow, G=Green, B=Blue, I=Indigo, and V=Violet.  This also orders the color by decreasing wavelength, with red having the longest wavelength and violet the shortest.

As sunlight passes through the atmosphere, the shorter waves are scattered more easily than the longer waves.  This has two important effects.  First, it shifts the color of the sun from white toward the longwave or "ROY" part of the spectrum.  Second, it shifts the color of the sky, which derives primarily from scattered sunlight, toward the shortwave or "BIV" part of the spectrum.

The strength of this shift depends on both the depth of the atmosphere and its constituents.  When the sun is high in the sky, it's usually yellow.  As the sun sets, sunlight follows a longer and longer path through the atmosphere, resulting in a gradual shift toward orange or even red.  The shift is stronger when there are smoke or pollution particles in the atmosphere, which are stronger scatterers than gas molecules.

A really horrible illustration of the longer path taken through the atmosphere by sunlight as the sun sets.
Geometry allows the transition to be especially rapid in the last few degrees of a sunset.  Here's a smoke-enhanced version of the orange to red shift as the smoke-enhanced sunset last night over Puget Sound.  Apologies for the change in magnification and somewhat crooked photos.

Here's a view of the orange sun between those two photos, which also shows a nice example of crepuscular rays higher in the sky.  Crepuscular rays are produced when scattered clouds produce alternating columns of shadowed and sunlight air.  The rays appear to radiate from the sun, but that's an illusion produced by perspective, much like train tracks to appear to converge at a distant point.